Mercury switch



Jan. l5, 1946: R. w. ALLISONl MERCURY SWITCH Filed Sepi. 7, 1943 M0441 .1NV,. ENI-MORT i PIM Patented Jan. 15, 1946 UNITED STATES PATENT GFFICE MERCURY SWITCH Robert Warren Allison, Atlanta, Ga. Application September 7, 1943, Serial No. 501,464

(Cl. 20G-33) 5 Claims.

This invention relates to an improved form of mercury switch, in which an accurate ytime delay is obtained between the tilting of the switch and the time the electrical contact is made, or broken, as the case may be.

Mercury switches are well known, and heretofore it has been proposed to so construct such switches that there is a time delay in the opening, or closing, of the electrical circuit. However, such switches either have been entirely inoperative, or somewhat less than satisfactory in operation, due to the fact that they either simply trapped the mercury in one end of the mercury tube of the switch and attempted to control its flow to the other end of the tube by restricting its ow -through a small orifice, or depended upon the force exerted-by the weight of the column of mercury to force a portion thereof through an orifice or restricted passage.

Those prior switches which depended solely upon the delay being caused by restricting the ow of the mercury through a small orifice, were inoperative as the molecular attraction,-or surface tension, of mercury is so high that it prevented the mercury from vflowing through a small orifice. If the orii'lce were made large enough so that the molecular attraction of the mercury did not too seriously interfere with the now of mercuryr therethrough, the desired delay'in opening, orclosing, the switch was not obtained.

The molecular attraction, or surface tension, of mercury is so great that it will support a column of mercury of about three-fourths of an inch in height over an opening of such size as to cause any appreciable delayed action in a mercury switch. Hence, in those prior switches in which the force exerted by the Weight of a column of mercury was utilized to force a portion of the mercury through a small orifice, such a large quantity of mercury was necessary to make the switch operative as to require the switch to be of impractical length to produce even a short delayed action, as the mercury would cease to flow through the restricted orifice, or passage,

ras soon as the force exerted by the hydrostatic head of the mercury decreased to an extent such that it became equal to the molecular attraction of the mercury over the opening. Thus, a substantial column of the mercury always was left in the upper end of the mercury tube. Furthermore, such switches were objectionable in that the hydrostatic head of the mercury caused the mercury which did pass through the restricted orice, or passage, to flow therethrough too rapidly and the electric circuit to be opened, or

closed, too soon. My experiments have indicated that to obtain a delay in the opening, or closing, of the electrical circuit as short as 15 seconds in such prior switches, a column of mercury of the order of four or ve inches in height and onefourth inch in diameter is necessary.

In accordance with my invention, there is provided a mercury switch in which 4the disadvantages of the prior mercury switches, as set forth above, are overcome, and a mercury switch is provided which is not of excessive length and which will give an accurate time delay between the tilting of the switch and the time the electrical circuit is opened, or closed.

In mercury switches constructed as hereinafter set forth, the force exerted by the molecular attraction of the mercury which normally would prevent the mercury from flowing through a small orifice, orA restricted passage, is equalized, and even used to facilitate the iiow of the mercury through the orice, or passage, thus enabling the desired time delay to be accomplished in a switch of relatively small size. As a matter of fact, a mercury switch about one'inch long and three-eighths inch in diameter, and constructed in accordance with my invention, can have a predetermined time delay period of anywhere from a few seconds to two minutes.

More specifically, my invention comprises a mercury switch in which mercury is caused to flow through a restricted orifice, or passage, from one end to the other of a tube of insulating material, as in prior mercury switches. However, the switch is so constructed and arranged that a pool of mercury is maintained at all times on both sides of the restricted orifice, or passage, regardless of the position to which the switch may be tilted in operation, and the orice is formed at the end of a relatively long tapering passage or nozzle, The amount of mercury in the switch is such that the passage or nozzle always is submerged in the mercury so that no air can enter thereinto. Thus, the molecular attraction of the mercury always tends to draw the mercury into the'pool at each side of the restricted oriiice, but the force is not suiiiciently great to break the mercury apart in the restricted orice and form a vacuum. A force equal to that exerted by a column of mercury 28 inches in length would be necessary to do that, and, of course, the molecular attraction of mercury is not that great. Thus, when the switch is tilted in the direction to cause a flow of mercury through the tapering passage toward the restricted orifice at the end thereof, the pull of the mercury already in the lower pool, plus the slight force exerted by the hydrostatic head of the mercury in the upper pool, is greater than the molecular' pull of the mercury in the upper pool, and the mercury will flow freely through the restricted orifice from the upper pool to the lower pool. The size of the restricted orifice at the end of the tapering passage is predetermined to so control the flow as to give the desired time delay before the electric circuit is opened, or closed The invention will be further described in connection with the accompanying drawing, but it is to be understood that such further disclosure is by way of exemplification and that the invention is not limited thereby.

In the drawing:

Fig. l is a longitudinal sectional view through a mercury switch embodying the present invention, and adapted to give a substantially instantaneous closing of the electrical circuit and a time delay between the tilting of the switch to its off position and the time the electrical circuit is broken, with the switch being shown in its full on position;

Fig. 2 is a longitudinal sectional View through the switch shown in Fig. l, with the switch being in its full oli position;

Fig. 3 is a view similar to Fig. 2, but showing the switch with the mercury passing through the restricted orifice from the upper pool to the lower pool after the switch has been tilted to its olf position and prior to the breaking of the circuit between the electrical contacts;

Fig. 4 is a longitudinal sectional View through a mercury switch embodying the present invention, and constructed to give a substantially instantaneous opening of the electrical circuit and a time delay between the tilting of the switch to the on position andthe time the contact between the electric circuit is made, with the switch being shown in its full olii position;

Fig. 5 is a longitudinal sectional view of the mercury switch in Fig. 4, with the switch being shown in its full on position; and

Fig. 6 is a longitudinal sectional View similar to Fig. 5, but showing the switch with the mercury passing through the restricted orifice from the upper pool to the lower pool during the time elapsing between the tilting of the switch to its on position and the bridging of the electrical contacts by the mercury.

It is apparent that the switch may be constructed to give either a substantially instantaneous bridging of the electrical contacts to close the electric circuit, and a delay between the time the switch is tilted to its off position and the opening of the electrical circuit, or a substantially instantaneous opening of the electrical circuit and a delay between the time the switch is tilted to its on position and the time the mercury bridges the electrical contacts to close the circuit.

A switch constructed to give a substantially instantaneous closing of the electrical circuit and a delay on the opening of the electrical circuit is shown in Figs. l, 2 and 3. Referring to those figures, therswitch comprises a tube I of any suitable material, such as glass, or other insulating material, mounted to be tilted between its on and oit positions. The means for tilting the switch form'no part of the present invention and arev not shown. When constructed of glass, the tube, after assembly of the several parts of the switch, may be flame-sealed, or the tube may be ofthe open-endedV type and have its open end hermetically sealed with sealing wax or other insulating material 2.

A funnel-shaped baille 3 having a spout l of relatively large diameter extending from its smaller end, is secured across the tube substantially midway of its length. The baille may be of metal or other material having its outer perimeter cemented 0r otherwise secured to the wall of the tube, or it may be formed integrally with the tube.

A pair of electrical contacts 5 and Q extend through the insulating sealing material 2, and have their ends positioned relatively close to the baille 3.

At one side, close to the perimeter thereof, the bafile 3 is provided with an elongated tapering passage or nozzle I which terminates in a small orifice 8. The passage or nozzle I extends from the baffle 3 at the side thereof opposite the electrical contacts 5 and 6. The tube is approximately'one-half filled with mercury and, when the tube is tilted in one direction, the mercury is adapted to submerge the electrical contacts 5 and- 6 and close the electric circuit of which they form a part. When the tube is tilted in the opposite direction, the mercury will flow away from the electrical contacts and open or break the electric circuit.

The space within the tube I which is not filled with mercury, is filled with nitrogen or some other inert gas, so that corrosion of the contacts will not occur.

The passage or nozzle 'I extends to near the proximate end of the. tube I and tapers to the orifice 8, which is of a size to sulliciently restrict the flow of mercury therethrough to give the desired time delay between the tilting of the switch to the off position, shown in Figs. 2 and 3, and the time the electrical circuit is opened by failure of the mercury any longer to bridgethe contacts 5 and 6. Y

The amountof mercury in the tube is suliicientv to maintain thepassage or nozzle 1- filled at all times, regardless of whether the switch is in the "on position shown in Fig. 1, or the 011 position shown in Figs. 2 and 3, so that the gas within the tube never Venters the nozzle to4 interfere with the flow of mercury through the restricted orifice 8.

With the switch in the on position shown in Fig. l, the electrical contactsare submerged in the mercury at the uppervend of the tube, at the right hand side of the baffle 3, with the result that the electrical circuitof which theA contacts 5. and 6 are a part, is closed. Also, when the switch isin that position, asubstantial amount of the mercury is at the4 lower endy of thetube. at the left hand side of the baille 3, and submerges the nozzle 1.

If theA switch is` now turned toits upright or ofi position shown in Figs. 2 and, 3, alarge portion of the `mercury is` trapped above, thebaie and is prevented by theI spout #from passing therethrough, except through therestricted oririce 8. When thetube is first tiltedA tosuch posi,

tion, the contacts 5 and Ii-are still welll submergedV in the mercury andthe electrical circuit remains closed.` Also, the` lower end of ther passage or nozzle, having the restricted orifice .8 at its end, is submergedy in the mercury inv thepool atthe bottom ofV the tube, so that themolecular attrac, tion of the mercury in the lowerpool tends tu draw the mercuryl from the upperpool through the orifice 8.v The force exerted by the'hydrostatic head` of .the mercury in the upper pool also tends. to force the mercury through the restricted4 orice 8, and as the combination of the force exerted by the hydrostatic head of the mercury in the upper pool and the force exerted by the molecular attraction of .the mercury in the lower pool, is greater than the molecular attraction of the mer- I cury in the upper pool, the mercury readily passes through the orifice, even when the oriiice isv made very small. After the desired time, predetermined by the size of the oriiice 8, the level of the mercury in the upper pool will have dropped to a position below the level of the electrical contacts 5 and 6 and the electrical circuit thereby broken. Such a condition is shown in Fig. 2. However, even when the ymercury has reachedits lowermost level, a portion I thereof still will remain on the upper side of the baille 3, above the uppermost part of the nozzle 1, so that none ci the gas within the tube can enter the nozzle.

If the switch is now tilted back to its on position, shown in Fig. 1, the mercury quickly spills through the spout 4 of the funnel-shaped baille 3, and almost instantaneously closes the electrical circuit by bridging the contacts and 6.

The switch shown in Figs. 4, 5 and 6, is constructed to give a substantially instantaneous opening of the electrical circuit, and atime delay between the tilting of the switch to on position and the time the electrical switch is closed. In the switch of those figures the passage or nozzle 'l' extends into the end of the mercury tube I' containing the electrical contacts 5 and 6', and the electrical contact 5 extends through a thickened portion l of the tube and enters the interior of the tube at a point near the baille 3', while the contact 6' extends through the insulating sealing material 2 at a point opposite the thickened portion I a of the tube, and terminates close to the insulating sealing material. Otherwise, the construction of the switch shown in Figs. 4, 5 and 6 is the same as the construction of the switch shown in Figs, l, 2 and 3, and the same reference characters, primed, are used to designate similar parts.

With the switch of Figs. 4, 5 and 6 in the position shown in Fig. 5, the electrical contact 6', which extends through the insulating sealing material at one side of the tube, is submerged in the mercury, but the electrical circuit is still broken.

as the electrical contact 5' is at the top of the tube, away from the mercury.

W'hen the switch is tilted from the off position shown in Fig. 4 to the on position shown in Figs. 5 and 6, a large portion of the mercury is trapped above the baille 3 by the spout 4', and can only pass to the bottom of the pool through the passage or nozzle I and the restricted orifice B at the bottom thereof. The condition of the switch just after being tilted to its on position, and before the electrical circuit has been completed by the mercury submerging the electrical contact 6', as well as electrical contact 5', is shown in Fig. 6. After a predetermined time, determined by the size of the orifice 8', most of -the mercury will have iiowed from the upper pool to the lower pool and submerged the contact 5 in the upper part of the lower portion of the tube, as well as the contact 6', with the result that the electrical circuit then is closed. The condition of the switch at such a time is shown in Fig. 5. However, even after the flow of mercury from the upper portion of the tube to the lower portion thereof has stopped, a portion I0 thereof will remain above the baille 3 and above the top of the nozzle or passage 1', so that none of the gas in the tube can enter the passage or nozzle to interfere with the flow of mercury through the oriilce 8 at the end thereof. It will. also be noted that in the switchof these gures, like in the switch of Figs. 1, 2 and 3, the passage or nozzle 1 and the oriiice 8 at the end thereof are completely submerged in the mercury at all times, regardless of which of its positions the switch is tilted.

If desired, one or both of the electrical contacts 5 and 6 of the switch of Figures 1, 2 and 3, or the electrical contact 5' of Figs. 4, 5 and 6, may be arranged to be adjustable longitudinally of the tube, so that the time delay between the opening or closing of the electrical circuit, as the case may be, may be varied for a switch having any size restricted oriiice for the passage of the mercury from one end of the tube to the other.

From the foregoing it will be readily understood that a switch constructed inv accordance with the present invention will give an accurate predetermined time delay between the time the switch is tilted to open, or close, the electrical circuit, and the time the electrical circuit actually is opened, or closed, depending upon the size of the restricted oriiice through which the mercury passes, due to the fact that the passage or nozzle having the restricted oriiice at the end thereof, is at all times completely submerged in the mercury within the tube, thus preventing the molecular attraction of the mercury from interfering with the free iiow of the mercury through the restricted passage, even when the restricted passage is made quite small. It will also be understood that by varying the size of the restricted oriilce at the end of the tapering passage or nozzle, the period of delay in the opening, or closing, of the electrical circuit may be varied over a substantial period of time.

What I claim is:

1. A delayed-action mercury switch comprising a tube adapted to be tilted to on and oil positions, a baille in said tube intermediate the length thereof, a pair of electrical contacts in the tube at one side of said baille, a body of mercury in the tube adapted upon tilting of the tube to make and break an electric circuit including said electrical contacts, the baille being adapted to trap a portion of the body of mercury when the tube is tilted to one of its positions, and an elongated tapering nozzle extending from the baille into one end of the tube, said nozzle forming a passage from one side of the baille to the other for mercury trapped by the baille when the tube is tilted to one of its positions, said nozzle terminating at its distal end in a restricted orice, the mercury in the tube completely filling the nozzle and submerging the restricted orice at all times, regardless of whether the tube is in its on or off position.

2. A delayed-action mercury switch comprising a tube adapted to be tilted to on" and off positions, a baille in said tube intermediate the length thereof, a pair of electrical contacts in the tube at one side of said baille, a body of mercury in the tube adapted upon tilting of `the tube to make and break an electric circuit including said electrical contacts, the baille being adapted to trap a portion of the body of mercury when the tube is tilted to one of its positions, and an elongated tapering nozzle extending from the baille, adjacent the periphery thereof, into one end of the tube, said nozzle forming a passage from one side of the baille to the other for mercury trapped by the baille when the tube is tilted to one of its positions, said nozzle terminating at its distal end in a restricted oriiice, the mercury in the tube completely llng the nozzle and submerging the restricted oriiice at all times, regardless of Whether the tube is in its on or oil position..

3. A delayed-action mercury switch comprising a tube adapted to be tilted to on and oil positions, a funnel-shaped baille extending across` said tube intermediate the length thereof, a pair of electrical contacts in the tube at one side of said baille, a body of mercury in the tube adapted upon tilting of .the tube to make and break an electricv circuitv including said electrical contacts, the baille being adapted to trap a portion of the body of mercury when the tube is tilted to one of its positions, and an elongated tapering nozzle extending from adjacent the periphery of the baille into one end of the tube, said nozzle forming a passage from one side of the baille to the other for mercury trapped by the baille when the tube is tilted to one of its positions, said nozzle terminating at its distal end in a restricted oriilce, the mercury in the tube completely filling the nozzle and submerging the restricted orifice at al1 times, regardless of Whether the tube is in its on or ofi position.

4, A delayed-action mercury switch comprising a tube adapted to be tilted to on and off positions, a baille in said tube intermediate the length thereof, a pair of electrical contacts in the tube at one side of said baille, a body of mercury in the tube adapted upon tilting of the tube to make and break an electric circuit including said electrical contacts, the baille being adapted to trap a portion of the body of mercury when the tube is tilted to one of its positions, and an elongated taperingnozzle extending from the baille adjacentthe periphery thereof into one end of the tube, said nozzle forming a passage from one side of the baille to the other for mercury trapped by the baille when the tube is tilted to one of its posh tions, said nozzle terminating at its distal end in a restricted orice, the electrical contacts heini in the end of the tube at the side of the baffle op` posite that end into which the nozzle extends, so that there is a time delay between the tilting ot the tube to the oiT position and the time the mercury ceases to bridge the electrical contacts, the mercury in the tube completely filling the nozzle and submerging the restricted oriilce at all times, regardless of whether the tube is in its on or off position.

5. A delayed-action mercury switch comprising a tube adapted to be tilted to on and on positions, a baille in said tube intermediate the length thereof, a pair of electrical contacts in the tube at one side of said baille, a body of mercury in the tube adapted upon tilting of the tube to make and break an electric circuit including said electrical contacts. the baille being adapted to trap a portion of the body of mercury when the tube is tilted to one of its positions, and an elongated tapering nozzle extending from the baille adjacent the periphery thereof into one end of the tube, said nozzle forming a passage from one side of the baille to the other for mercury trapped by the baflie when the tube is tilted to one of its positions, said nozzle terminating at its distal end in a restricted orifice, the electrical contacts being in the end of the tube into which the nozzle extends and in diilerent horizontal planes so that there is a time delay between the tilting of the switch to the on position and the bridging of the contacts by the mercury, the mercury in the tube completely filling the nozzle and submerging the restricted orifice at all times, regardless of whether the tube is in its on or off position,

ROBERT WARREN ALLISON. 

